First of all congratulations on choosing the Mk16SV which is the second best long range assault rifle, only superseded by the AR-21 SV.
Second, (disclaimer: personal opinion, no offense anyone) the Phantom 1-4x sight is just shit.
You can't see anything left or right of it.
You can see quite little in the middle because of the barrel of your own gun.
You will try to snipe an enemy far away and will find that your sight is in 1x mode. You click your "toggle zoom mode" button. You zero in on the enemy. And you died 3 seconds ago because of being out in the open and fumbling with your scope.
You will try to shoot someone in close quarters and will find that your sight is still in 4x mode. You won't see anything. You will be shot. You will look like an idiot.
You will either revert to the Assault 3.5x or buy the SUSAT 4x scope.
I had mine on my Mk16 for about 2 hours. Then I was sick of it. Now I use the SUSAT. It's as no-nonsense as it looks. Have noticed no drawbacks yet (and I've been using it for 2 months now).
Also see
here, 3rd post.